I’ve first used Manapro Unimilk which is powered milk primarily for livestock (because we had it for the horses). It worked nicely with granola. Saved an 8oz plastic baby food jar to mix it with. Shake, shake, shake and pour. Unfortunately it only comes in large bags (like 9lbs or more) so, even in the freezer, it aged out and was disposed. Last trip I tried Carnation Malted Milk (powered) and was very pleased. Too sweet for some folks but, when preparing for 30 or so loaded miles before lunch, the carbs set well with me. I don’t recall the powder to water ratio I use but you just conduct experiments at home to find what suits you. I have a 13oz jar which reseals well and seems to have good shelf life.